The present invention relates to a fuel injection apparatus and, more particularly, to a fuel injection apparatus provided with a plurality of intake tubes for supplying an air-fuel mixture to an engine having a plurality of cylinders.
Engines having a relatively large piston displacement are generally constructed as V-engines or horizontally opposed engines for the purpose of reducing the size and weight of the engines. To supply an air-fuel mixture to these engines with high accuracy, in, for example, U.K. Patent application No. GB 2,082,252 A, a fuel injection apparatus is proposed wherein a plurality of intake tubes and a plurality of fuel injection valves, respectively corresponding to the plurality of intake manifolds are provided, with the intake tubes being respectively provided with throttle valves, adapted to be simultaneously opened or closed. A hot-wire type air flowmeter measures the quantity of air sucked into the intake tubes, and the detection portion of the air flowmeter is disposed in a by-pass passage which allows a quantity of air to pass that is proportional to the quantity of air sucked into the intake tubes.
The fuel above proposed fuel injection apparatus is arranged such that the outlets of the by-pass passage are respectively disposed inside the intake tubes but inlets of the by-pass passage are respectively disposed outside the intake tubes. For this reason, the intake air pulsation produced by the operation of the engine is transmitted also to the by-pass passage, causing disorder of the output of the hot-wire type air flowmeter. Accordingly, there is a reduction in accuracy in the measurement of the quantity of air which is actually sucked into the engine, so that the quantity of fuel injected by each of the fuel injection valves, controlled by the output of the hot-wire type air flowmeter, deviates from the amount actually necessary thus causing the control of air-fuel ratio to deteriorate and the fuel combustibility in the cylinders of the engine to be impaired, disadvantageously lowering exhaust characteristics, performance and output of the engine and increasing fuel consumption.
Accordingly, it is an object of the present invention to provide a fuel injection apparatus which increases the measurement accuracy of the quantity of intake air effected by the hot-wire type air flowmeter which has a hot-wire or resistance layer as a detection portion thereof and enable a high accurate fuel injection required for the measured quantity of air.
To this end, according to the invention, a fuel injection apparatus comprises a plurality of intake tubes each having a throttle valve; a fuel injection valve for injecting fuel into each of the intake tubes; a hot-wire type air flowmeter for measuring the quantity of intake air sucked into the intake tubes; and a by-pass passage which accommodates the detection portion of the hot-wire type air flowmeter. The by-pass passage has an inlet portion for introducing the static pressure of flow of the intake air sucked into each intake tube, a central portion for passing en bloc the air introduced from each of the intake tubes and an outlet portion for discharging into each intake tube the air passing through the central portion, with the detection portion of the hot-wire type air flowmeter being disposed in the central portion of the by-pass passage.
Each of the inlets of the by-pass passage is preferably provided in the side wall of an injector holder accommodating the corresponding fuel injection valve or the side wall of the corresponding intake tube.